CN105648386B - Thermal spraying aluminium oxide-yttrium oxide composite ceramic coat and preparation method thereof - Google Patents

Abstract

The invention relates to a thermal sprayed alumina-yttria composite ceramic coating and a preparation method thereof. The alumina-yttria composite ceramic coating is formed on a metal substrate or on a stress transition layer located on the surface of the metal substrate. And the alumina-yttrium oxide composite ceramic coating includes α-Al ₂ O ₃ phase, γ-Al ₂ O ₃ phase, c-Y ₂ O ₃ phase, m-Y ₂ O ₃ phase and the The Y _x Al _y O _z phase generated in situ by yttrium, said Y _x Al _y O _z is Y ₃ Al ₅ O ₁₂ , Y ₄ Al ₂ O ₉ and/or YAlO ₃ , wherein the α-Al ₂ O ₃ phase is associated with The mass ratio of the γ-Al ₂ O ₃ phase is 1: (2-3). The aluminum oxide-yttrium oxide composite ceramic coating prepared by a thermal spraying process in the invention has a dense coating structure and low porosity. There is no solid solution between Al ₂ O ₃ and Y ₂ O ₃ , and Y _x Al _y O _z compounds can be formed in situ during the spraying process, which plays the role of dispersion toughening and strengthening the phase interface, and the interlayer interface of the coating is relatively bonded. Well, toughness and thermal shock resistance are improved.

Description

Thermal spraying alumina-yttrium oxide composite ceramic coating and preparation method thereof

technical field

The invention relates to a thermal spraying alumina-yttrium oxide composite ceramic coating and a preparation method thereof, belonging to the technical field of wear-resistant ceramic coatings.

Background technique

Oxide ceramic materials have the characteristics of high strength, high hardness, wear resistance, high temperature resistance, oxidation resistance, corrosion resistance, etc., and show good comprehensive performance. They are used as thermal spray coating materials for high specific pressure (ie high PV value : P is the contact pressure; V is the friction rate), high temperature, oxygen-enriched, strong thermal shock, strong corrosion and other harsh wear service conditions have good potential, and can combine the advantages of metal substrate and oxide ceramic coating, Good engineering applications are expected. However, oxide ceramics have low ductility and high crack sensitivity, which restrict their applications. Previous related research mainly focused on improving the strength and toughness of oxide ceramics, including the following aspects: ① Particle toughening, including the toughening of metal particles in the tough phase and the toughening of ceramic particles in the hard phase. The granular materials commonly used for toughening _oxide ceramics mainly include Ni, Al, Cu, SiC, TiC, TiB2, etc. The addition of the ductile metal phase can release the stress concentration at the crack tip, the corresponding cracks in the crack tip area are not easy to form, and the crack propagation resistance increases, that is, the fracture toughness of the material is improved; the addition of the hard ceramic phase can refine the matrix crystal Particle and crack shielding effect, dissipate the force of crack advancement, and achieve the purpose of toughening. The process is simple and easy, and the cost is low. When the parameters such as the type, size, and content of the particles are properly selected, the toughening effect is more obvious. In order to achieve a good toughening effect, particle nanoscale is the development direction. ②Fiber (or whisker) toughening, when high-strength fiber (or whisker) is dispersed in the ceramic matrix as the second phase, toughening is carried out in two ways. One is to make the crack propagation path appear inflection phenomenon, thereby increasing Fracture energy; the second is that when the fiber (or whisker) is pulled out from the matrix, part of the energy is consumed in the form of pulling work, which is beneficial to prevent the crack from expanding. Fibers (or whiskers) commonly used for toughening oxide ceramics include SiC fibers (or whiskers), Si ₃ N ₄ whiskers, carbon fibers, and B fibers. ③Phase transformation toughening, it is to use tetragonal phase (t phase) ZrO ₂ martensitic phase transformation into monoclinic phase (m phase) ZrO ₂ to absorb more energy due to the volume and shape effect, so that the oxide Ceramic materials exhibit high fracture toughness. ④Composition or structure gradient toughening, forming a gradient material through composition or structure changes, can basically eliminate the macroscopic interface, effectively solve the sudden change in the internal properties of the material, and achieve the purpose of relieving thermal stress.

Thermal spraying technology has become an effective method for preparing ceramic coatings due to its wide range of spraying materials, wide range of substrate deposition temperature, controllable coating thickness and large range (several microns to several mm), good process stability, and reliable coating quality. It has been widely used in aerospace, aviation, automobile, machinery, energy, metallurgy, petrochemical, shipbuilding, etc. The above four typical ceramic toughening methods have their own characteristics, and have shown good toughening effects on ceramic composite blocks. However, when these methods are combined with thermal spraying technology, they have obvious limitations. In: ① For ceramic composite blocks, particle toughening should achieve a better toughening effect, and its average particle size should be submicron or nanometer. The plasma spraying process is widely used in the preparation of thermal sprayed ceramic coatings, and plasma spraying is a rapid solidification process. The grain size of the sprayed ceramic coating is usually submicron, and the toughening effect of the particles on the composite coating is not obvious. Better results are expected to be obtained if nanoparticles with smaller particle sizes are used for toughening. Nanoparticles sprayed and granulated can exist in the composite coating structure, but the proportion of nanoparticles in the coating grain boundary or inside the grain is difficult to control, the strength and toughness of the composite coating vary widely, and the repeatability of mechanical properties is poor, so it cannot be effectively improved. Ceramic coating toughness. ② Although fiber (or whisker) toughening can improve the mechanical properties of the coating, its aspect ratio must be large, and the fiber (or whisker) must maintain a moderate bonding strength with the matrix. However, during the thermal spraying process, the particles are in a molten or semi-molten state, and the original aspect ratio, surface functionalization and strength of the fibers (or whiskers) are difficult to guarantee. When nanofibers (or whiskers) are incorporated, problems similar to those faced by the aforementioned nanoparticles are also encountered. Therefore, fiber (or whisker) toughening is difficult to effectively combine with thermal spraying process. ③ ZrO ₂ (YSZ) partially stabilized by adding ZrO ₂ or Y ₂ O ₃ can also be used to toughen ceramic coatings. The problem caused by this is: ZrO ₂ or YSZ has low thermal conductivity and large thermal expansion coefficient. Thermal stress accumulates on the substrate interface, and stress concentration leads to the expansion of microcracks in the coating, which shortens the wear life of the composite ceramic coating. ④ Gradient coating toughening often requires the preparation of more single layers for superimposition. The thickness of each single layer is limited, and different composition or structure control is required. Hardness and strength are not yet ideal.

It is difficult to effectively improve the strength and toughness of oxide ceramic coatings by combining the above traditional ceramic toughening methods with thermal spraying technology. Among single-component oxide wear-resistant ceramic coatings, the wear resistance of Al ₂ O ₃ and Cr ₂ O ₃ coatings is better than that of ZrO ₂ coatings. Under severe wear conditions, the wear resistance of Al ₂ O ₃ coatings is better than that of Cr ₂ O ₃ coatings, which is mainly due to the higher thermal conductivity of the former. Therefore, the current strengthening and toughening research focuses more on thermal spraying Al ₂ O ₃ coatings, mainly including: ① Nano-sized raw material particles. The mechanical properties of the coating obtained by using spray granulated nano-Al ₂ O ₃ particles as raw materials are better than those corresponding to traditional micron-sized particles. ② Add metal phase. The addition of second-phase metals (such as Al, Ni, Mo, etc.) improves the fracture toughness and thermal conductivity of Al ₂ O ₃ coatings, showing better wear resistance. ③ solid solution toughness. More typical are Al ₂ O ₃ -TiO ₂ and Al ₂ O ₃ -Cr ₂ O ₃ systems. The melting point of TiO ₂ is low, and the formed solid solution and part of TiO ₂ are easy to gather at the grain boundary of Al ₂ O ₃ coating, which can improve the internal bonding force of the coating layer and inhibit the transverse crack propagation. Al ₂ O ₃ –Cr ₂ O ₃ composite coatings show better mechanical, thermal conductivity and wear resistance properties than single Al ₂ O ₃ coatings. The research on improving the strength and toughness of Al ₂ O ₃ coatings has made some progress, but there are still some problems: ①The high frictional heat generated under harsh wear conditions leads to the instability of the nanostructure of the coating; ②The grain boundaries of nanostructured ceramic coatings are relatively weak. If there are many, it has a great effect on phonon scattering, resulting in a decrease in thermal conductivity, which is not conducive to the application under harsh wear conditions; ③Adding a metal phase will reduce the hardness and strength of the coating, which is not conducive to its service under harsh conditions, and the metal phase It is difficult to control the interface bonding performance with the ceramic substrate; ④The addition of TiO ₂ reduces the high-temperature creep resistance of the coating and the high-temperature mechanical properties; Solid solution structure and properties in coatings.

Contents of the invention

The technical problem to be solved by the present invention is to provide a thermal sprayed alumina-yttrium oxide composite ceramic coating and a preparation method thereof for the shortcomings of the above-mentioned prior art. Improving the compactness, mechanical properties, thermal conductivity, interlayer bonding performance and wear resistance of ceramic coatings under harsh wear conditions such as impact can avoid the previous nanostructure, metal second phase addition, and compound solid solution effects in the above harsh conditions. Detrimental effects of abrasive conditions on the performance and service life of ceramic coatings.

In order to achieve this purpose, the present invention provides an alumina-yttria composite ceramic coating, which is formed on a metal substrate or on a stress transition layer located on the surface of a metal substrate , and the alumina-yttria composite ceramic coating includes α-Al ₂ O ₃ phase, γ-Al ₂ O ₃ phase, cY ₂ O ₃ phase, mY ₂ O ₃ phase and The Y _{x Aly O z phase generated by the position, the Y x Aly O z is Y 3} Al ₅ O ₁₂ , Y ₄ Al ₂ O ₉ and/or YAlO ₃ , wherein the α-Al ₂ O ₃ phase and the γ- The mass ratio of the Al ₂ O ₃ phase is 1:(2-3).

The alumina-yttria composite ceramic coating provided by the present invention includes the Y _{x AlyOz} phase generated in situ by alumina and yttrium oxide, and the _{Y x AlyOz phase} can act as a dispersion toughening and strengthening phase The role of the interface, the interface between the coating layers is well bonded, and the strength, toughness and thermal shock resistance are improved. It can avoid the nano-coating structure, metal second phase addition, and solid solution effect that may affect the mechanical properties, microstructure stability, and service life of ceramic coatings under severe wear conditions such as high load, high temperature, oxygen-enriched, and strong thermal shock. adverse effects. And the content of α-Al ₂ O ₃ phase in the composite coating of the present invention is significantly increased, and the thermal conductivity and strength of α-Al ₂ O ₃ are better than γ-Al ₂ O ₃ , and the introduced Y ₂ O ₃ itself The thermal conductivity of the composite ceramic coating is also good, which will improve the thermal conductivity of the composite ceramic coating and reduce the thermal stress caused by the difference in thermal expansion coefficient between the ceramic coating and the metal substrate, thereby alleviating the expansion of micro-cracks inside the coating and improving Wear resistance and effective life of ceramic coatings under severe abrasive service conditions.

Preferably, the mass fraction of the α-Al ₂ O ₃ phase is 9-24%.

Preferably, the mass fraction of the cY ₂ O ₃ phase is 9-29%, and the mass ratio of the mY ₂ O ₃ phase to the cY ₂ O ₃ phase is 1:(3-4).

Preferably, the mass fraction of the _{YxAlyOz phase} is _6-10 %.

Preferably, the thickness of the alumina-yttrium oxide composite ceramic coating is 250-500 μm.

The present invention also provides a method for preparing an alumina-yttrium oxide composite ceramic coating, comprising:

(1) Carrying out pretreatment to the metal substrate, including roughening and purifying the pre-sprayed surface of the metal substrate;

(2) Alumina powder and yttrium oxide powder are mechanically mixed to obtain a composite powder;

(3) Deposit the composite powder obtained in (2) on the surface of the pretreated metal substrate obtained in (1) by thermal spraying to obtain the alumina-yttria composite ceramic coating; or before depositing the composite powder Firstly, the stress transition layer is sprayed on the surface of the pretreated metal substrate obtained in (1), and then the composite powder obtained in (2) is deposited on the stress transition layer by thermal spraying to obtain the alumina-yttria composite ceramic coating Floor.

Preferably, the metal substrate is stainless steel, alloy or metal matrix composite material, the roughened surface roughness Ra of the metal substrate is 5-10 μm, and the stress transition layer is nickel chromium (NiCr) or nickel Aluminum (NiAl) alloy with a thickness of 40-100 μm.

Preferably, the mass fraction of the alumina powder in step (2) is 20%-40% of the composite powder, and the particle size is 15-45 μm.

Preferably, the particle size of the yttrium oxide powder in step (2) is 15-45 μm.

Preferably, the thermal spraying in step (3) is plasma spraying, and the plasma spraying process parameters are: plasma gas argon flow rate 40-50 slpm, plasma gas hydrogen flow rate 6-10 slpm, current 630-690A, power 45- 50kW, powder feeding carrier gas argon flow rate 3~4slpm, powder feeding rate 30~40g/min, spraying distance 100~120mm. Where slpm is an abbreviation for standard liters per minute.

Preferably, the powder particle size distribution range of the stress transition layer in step (3) is 35-65 μm, the stress transition layer is sprayed by plasma spraying, and the plasma spraying process parameters are: plasma gas argon flow rate 50 ~70slpm, plasma gas hydrogen flow rate 8~12slpm, current 550~620A, power 40~45kW, powder feeding carrier gas argon flow rate 3~4slpm, powder feeding rate 20~30g/min, spraying distance 110~130mm. Where slpm is an abbreviation for standard liters per minute.

The aluminum oxide-yttrium oxide composite ceramic coating prepared by a thermal spraying process in the invention has a dense coating structure and low porosity. There is no solid solution between Al ₂ O ₃ and Y ₂ O ₃ , and Y _x Al _y O _z compounds can be formed in situ during the spraying process, which plays the role of dispersion toughening and strengthening the phase interface, and the interlayer interface of the coating is relatively bonded. Well, toughness and thermal shock resistance are improved.

During the spraying process, the addition of Y ₂ O ₃ is beneficial to the stability of the α-Al ₂ O ₃ phase in the coating. Therefore, compared with the single alumina coating, in the phase composition of the alumina-yttria composite ceramic coating, The content ratio of α-Al ₂ O ₃ phase to γ-Al ₂ O ₃ phase increases significantly, and the thermal conductivity and strength of α-Al ₂ O ₃ are better than that of γ-Al ₂ O ₃ , while Y ₂ O ₃ itself has The thermal conductivity is also good, which will improve the thermal conductivity of the composite ceramic coating and reduce the thermal stress caused by the difference in thermal expansion coefficient between the ceramic coating and the metal substrate, thereby alleviating the expansion of micro-cracks inside the coating and improving the ceramic coating. The wear resistance and effective life of coatings under severe abrasive service conditions.

Description of drawings

Figure 1 is the SEM morphology of two powders: (a) alumina; (b) yttrium oxide;

Fig. 2 is the X-ray diffraction pattern of aluminum oxide-yttrium oxide composite powder and coating;

Fig. 3 is the scanning electron microscope morphology of the polished cross-section of composite ceramic coatings with different yttrium oxide contents: (a) 30%; (b) 20%; (c) 40%;

Fig. 4 is that yttrium oxide content is the component analysis of the composite ceramic coating section of 30%;

Figure 5 is a comparison photo of alumina coating and alumina-yttrium oxide composite ceramic coating before and after thermal shock (500°C for 30 minutes and water quenching for a total of 40 times): (a) alumina coating; (b) alumina - Yttrium oxide composite ceramic coating (the mass fraction of yttrium oxide is 40%);

Fig. 6 is the room temperature thermal conductivity and thermal diffusivity of alumina coating, yttrium oxide coating and alumina-yttrium oxide composite ceramic coating (yttrium oxide mass fraction is 20%);

Fig. 7 is the friction coefficient curve over time obtained by pairing alumina coating and alumina-yttrium oxide composite ceramic coating with graphite for high-load wear test (ring-block wear mode, load 1000N, friction speed 0.84m/ s, wear time 60min);

Figure 8 is the respective wear rates of the coating and graphite in the wear test of the alumina coating and the alumina-yttria composite ceramic coating (the mass fraction of yttrium oxide is 20%) paired with graphite;

Figure 9 is the wear surface morphology of alumina coating and alumina-yttria composite ceramic coating (30% yttrium oxide mass fraction): (a) Al ₂ O ₃ ; (b) Al ₂ O ₃ -30wt% Y ₂ O ₃ ;

Fig. 10 is the friction coefficient curve (ring-block wear mode, load 1000N, friction speed 0.84m/s, wear time 60min).

Detailed ways

The following embodiments further illustrate the present invention. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

The present invention uses Al ₂ O ₃ and Y ₂ O ₃ as raw materials to prepare an alumina-yttria composite ceramic coating, and the following examples illustrate the preparation method of the alumina-yttria composite ceramic coating.

The pretreatment of the metal substrate may include roughening and purifying the pre-sprayed surface of the metal substrate. Wherein, the metal substrate can be stainless steel, alloy or metal matrix composite material. After roughening the surface of the metal substrate, the surface roughness Ra of the metal substrate after roughening is 5-10 μm, and the roughening is beneficial to improve the bonding performance between the sprayed coating and the metal substrate. Then the surface of the metal substrate is purified. As an example, the 2Cr13 stainless steel substrate can be selected to be sandblasted with 20# white corundum sand at a working pressure of 0.4-0.5MPa, then ultrasonically cleaned with ethanol for 5 minutes, and then dried with compressed air.

The alumina powder and yttrium oxide powder are mechanically mixed to obtain a composite powder for subsequent spraying. Wherein, the mass fraction of the yttrium oxide powder can be 20%-40% of the composite powder. The addition of Y ₂ O ₃ is beneficial to the stability of the α-Al ₂ O ₃ phase in the coating, and the thermal conductivity and strength of α-Al ₂ O ₃ are better than those of γ-Al ₂ O ₃ , while the thermal conductivity of Y ₂ O ₃ itself The performance is also better, which will improve the thermal conductivity of the composite ceramic coating and reduce the thermal stress caused by the difference in thermal expansion coefficient between the ceramic coating and the metal substrate, thereby alleviating the expansion of micro-cracks inside the coating and improving the ceramic coating. The wear resistance and effective life of the layer under harsh wear service conditions. When the content of yttrium oxide is less than 20% (such as 0%), the above-mentioned coating performance improvement effect cannot be achieved, and when the content of yttrium oxide exceeds 40% (such as 60%), the hardness of the composite coating drops greatly, which is not conducive to high-load harsh wear Serve under conditions. The particle size of yttrium oxide is 15-45 μm, and the particle size of alumina powder is 15-45 μm. Appropriate particle size distribution range is conducive to ensuring the quality of sprayed coatings. When the particle size is less than 15μm, the fluidity of powder transportation begins to deteriorate, and some fine powder may block the nozzle of the spray gun, and randomly fly out large agglomerated particles that remain in the coating and cause cracks and holes. Melting, when spreading and depositing on the surface of the substrate, sputtering-type spreading morphology will appear, and the bonding strength is not good; when the particle size is larger than 45 μm, the powder may be insufficiently melted, so that a large amount of unmelted powder will be left in the spraying process. Particles, resulting in poor bonding within the coating sheet, and then the coating's mechanical and wear resistance properties are reduced. The types of alumina and yttrium oxide powders can be, but not limited to, one of melt crushing, agglomeration and sintering, spheroidizing and spray drying.

The composite powder is deposited on the surface of the pretreated metal substrate by thermal spraying to obtain the alumina-yttrium oxide composite ceramic coating. The thermal spraying can be but not limited to plasma spraying, detonation spraying or supersonic flame spraying can also be used. As an example, the plasma spraying process parameters are: plasma gas argon flow rate 40~50slpm, plasma gas hydrogen flow rate 6~10slpm, current 630~690A, power 45~50kW, powder carrier gas argon flow rate 3~4slpm, The powder rate is 30-40g/min, and the spraying distance is 100-120mm. The thickness of the obtained coating can be 250-500 μm. The choice of coating thickness is conducive to service under harsh wear conditions. If the coating thickness is too large, the stress will accumulate during the spraying process, and the coating may sinter if the spraying time is long. The mechanical and wear-resistant properties are reduced; the service life of the coating is reduced during the wear process if the coating thickness is too small. In addition, the thickness is too small to bring difficulties to the uniformity of grinding and polishing in the later stage.

Or it is also possible to spray a stress transition layer on the surface of the pretreated metal substrate before depositing the composite powder, and then deposit the resulting composite powder on the stress transition layer to obtain the alumina-yttrium oxide composite ceramic coating . The particle size distribution range of the nickel-chromium (NiCr) or nickel-aluminum (NiAl) alloy powder in the stress transition layer is 35-65 μm. The spraying of the stress transition layer may be, but not limited to, plasma spraying, vacuum plasma spraying, supersonic flame spraying and the like. As an example, the process parameters of plasma spraying are: plasma gas argon flow rate 50-70 slpm, plasma gas hydrogen flow rate 8-12 slpm, current 550-620A, power 40-45kW, powder carrier gas argon flow rate 3-4 slpm, The powder feeding rate is 20-30g/min, and the spraying distance is 110-130mm.

The stress transition layer can be nickel-chromium (NiCr) or nickel-aluminum (NiAl) alloy. Studies have shown that under high load (ie high PV value) combined with severe wear and service conditions (often accompanied by high temperature, strong oxidation, and large thermal shock), the friction generated The heat increases suddenly, and the higher the thermal conductivity of the coating, the easier it is to transfer this heat to the metal substrate and dissipate heat to the surrounding environment. The addition of the stress transition layer can further effectively control the temperature gradient between the friction surface and the metal substrate, so that the thermal stress caused by the difference in thermal expansion coefficient between the coating and the substrate is small, so the coating is not easy to crack or peel off On the contrary, if there is no stress transition layer, the thermal stress concentration will easily cause the microcracks inside the coating to expand rapidly. During the fatigue wear process, the coating is prone to cracking or peeling off, resulting in a sharp decrease in its wear resistance. The thickness of the stress transition layer is 40-100 μm. If the thickness is too large, the stress accumulation will be large, which is not conducive to the wear and service of the ceramic layer; if the thickness is insufficient, the spraying will be uneven, the performance of the stress transition layer will be reduced, and the stress adjustment effect cannot be fully displayed.

The alumina-yttrium oxide composite ceramic coating prepared by the present invention is analyzed by X-ray diffraction, including α-Al ₂ O ₃ phase, γ-Al ₂ O ₃ phase, cY ₂ O ₃ phase and mY ₂ O ₃ phase, in addition In addition, it also includes the Y _x Al _y O _z phase generated in situ during the thermal spraying process from mutually insoluble alumina and yttrium oxide, such as Y ₃ Al ₅ O ₁₂ (YAG), Y ₄ Al ₂ O ₉ (YAM ) or YAlO ₃ (YAP) are equivalent. The content of α-Al ₂ O ₃ phase is significantly higher than that of single alumina coating, because the addition of Y ₂ O ₃ is beneficial to the stability of α-Al ₂ O ₃ phase in the coating during the spraying process. The total content of the cY ₂ O ₃ phase and the mY ₂ O ₃ phase can be determined according to the amount of Y ₂ O ₃ raw material powder added. The _{Y x} Aly O _z compound formed in situ can play the role of dispersion toughening and strengthening the phase interface, the interlayer bonding of the coating is better, and the strength, toughness and thermal shock resistance are improved. It can avoid the nano-coating structure, metal second phase addition, and solid solution effect that may affect the mechanical properties, microstructure stability, and service life of ceramic coatings under severe wear conditions such as high load, high temperature, oxygen-enriched, and strong thermal shock. adverse effects.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Thermal spraying aluminum oxide-yttrium oxide composite ceramic coating and preparation method thereof, the method comprises the following steps:

(1) Pretreatment of the metal substrate, including: roughening and purification of the pre-sprayed surface of the metal substrate. Two kinds of 2Cr13 stainless steel substrates: ①Square piece (30mm×15mm×1.25mm); ②Circular ring (Φ40mm×Φ16mm×10mm) is first sandblasted with 20# white corundum sand, and the working pressure is 0.4 ~0.5MPa, then ultrasonic cleaning with ethanol for 5 minutes, and then dry it with compressed air. The average surface roughness Ra of the stainless steel substrate after pretreatment is 7.32 μm;

(2) Aluminum oxide-yttrium oxide composite ceramic coating is deposited on the surface of the treated metal substrate by thermal spraying process. First, the aluminum oxide powder with a particle size of 15-45 μm and the yttrium oxide powder with a particle size of 15-45 μm were mechanically mixed for 48 hours by drum type to obtain a uniformly dispersed composite powder, wherein the mass fraction of the yttrium oxide powder was 30%. Alumina powder is fused and crushed, and yttrium oxide powder is agglomerated and sintered (see Figure 1). The phases of the above two powders are α-Al2O3 and c-Y2O3 respectively (see Figure 2). The nickel-chromium alloy stress transition layer is first sprayed on the surface of the treated 2Cr13 stainless steel substrate. The particle size distribution range of the alloy powder is 35-65 μm. The plasma spraying process is adopted. The specific parameters are as follows: plasma gas argon flow rate 60slpm, plasma gas hydrogen The flow rate is 8slpm, the current is 580A, the power is 42kW, the powder delivery carrier gas argon flow rate is 3slpm, the powder delivery rate is 20g/min, and the spraying distance is 120mm. In addition to the above atmospheric plasma spraying, vacuum plasma spraying, supersonic flame spraying, etc. can also be used. The thickness of the nickel-chromium alloy layer is 60-80 μm. Then plasma spray alumina-yttrium oxide composite ceramic coating on the surface of the nickel-chromium alloy bonding layer. The spraying process parameters are: plasma gas argon flow rate 45slpm, plasma gas hydrogen flow rate 9slpm, current 650A, power 46kW, powder delivery carrier gas The argon gas flow rate is 4 slpm, the powder feeding rate is 35g/min, and the spraying distance is 110mm. In addition to the above atmospheric plasma spraying, explosive spraying or supersonic flame spraying can also be used. The thickness of the composite ceramic coating is 440-460 μm. The obtained composite ceramic coating contains α-Al2O3, γ-Al2O3, c-Y2O3 and m-Y2O3 phases (see Figure 2). The mass ratio of α-Al2O3 to γ-Al2O3 is 1:2, while the mass ratio of α-Al2O3 to γ-Al2O3 in a single alumina coating is 1:9. This shows that the phase stability of α-Al2O3 in alumina-yttria composite ceramic coating prepared by spraying is better, which will help to improve the mechanical and thermal conductivity of the coating.

The polished cross-sectional morphology of the prepared alumina-yttrium oxide composite ceramic coating shows that the coating has low porosity and high density, and the interface between the ceramic coating, nickel-chromium alloy layer and stainless steel substrate is well bonded (see Fig. 3). Composition analysis showed that Al ₂ O ₃ and Y ₂ O ₃ formed Y ₃ Al ₅ O ₁₂ and Y ₄ Al ₂ O ₉ compounds in situ during the spraying process (see Figure 4). Among them, the mass fraction of α-Al ₂ O ₃ phase is 18%, the mass fraction of γ-Al ₂ O ₃ phase is 45%, the mass fraction of cY ₂ O ₃ phase is 22%, and the mass fraction of mY ₂ O ₃ phase is 6%, The mass fraction of the Y ₃ Al ₅ O ₁₂ phase is 4%, and the mass fraction of the Y ₄ Al ₂ O ₉ phase is 5%. Combined with the cross-sectional morphology of the coating and the results of energy spectrum analysis, it is proved that there is no solid solution between Al ₂ O ₃ and Y ₂ O ₃ , and the compound can be formed in situ during the spraying process, which will play a role in dispersion toughening and strengthening of the phase interface. The interface between the coating layers is well bonded, which is conducive to the improvement of its toughness and thermal shock resistance.

Further, the wear resistance of alumina-yttria composite ceramic coatings under high load conditions was investigated. The ring-block wear method (the coating is deposited on the surface of the outer edge of the ring), dry friction conditions, load 1000N, friction speed 0.84m/s (rotation speed 400rpm), wear time 60min, the grinding material is graphite block (30mm× 7mm×6mm), and compared with a single alumina coating. The test results show that the friction coefficient of the alumina-yttria composite ceramic coating/graphite friction pair is very low, and the numerical stability is good, with an average value of μ = 0.045, which is significantly better than that of the single alumina coating (see Figure 7). The wear surface morphology shows that after wear, the surface of the alumina-yttria composite ceramic coating has almost no wear marks except for the graphite phase residue. However, there are obvious white stripe wear marks on the worn surface of the single alumina coating (see Figure 9). In summary, the alumina-yttria composite ceramic coating has better wear resistance.

Example 2

Thermal spraying aluminum oxide-yttrium oxide composite ceramic coating and preparation method thereof, the method comprises the following steps:

(1) Pretreatment of the metal substrate, including: roughening and purification of the pre-sprayed surface of the metal substrate

The metal substrate selection and pretreatment method are the same as in Example 1. After pretreatment, the average surface roughness Ra of the stainless steel substrate was 6.56 μm. The square sample is used for section morphology observation and thermal shock test, and the ring sample is used for friction and wear test;

(2) Aluminum oxide-yttrium oxide composite ceramic coating is deposited on the surface of the treated metal substrate by thermal spraying process

The preparation method of selecting the composite powder is the same as that of Example 1, except that the mass fraction of yttrium oxide powder is 40%. The nickel-chromium alloy stress transition layer is first sprayed on the surface of the treated 2Cr13 stainless steel substrate. The particle size distribution range of the alloy powder is 35-65 μm. The plasma spraying process is adopted. The specific parameters are as follows: plasma gas argon flow rate 55slpm, plasma gas hydrogen The flow rate is 9slpm, the current is 600A, the power is 43kW, the powder delivery carrier gas argon flow rate is 3.5slpm, the powder delivery rate is 22g/min, and the spraying distance is 120mm. In addition to the above atmospheric plasma spraying, vacuum plasma spraying, supersonic flame spraying, etc. can also be used. The thickness of the nickel-chromium alloy layer is 60-80 μm. Then plasma spray alumina-yttrium oxide composite ceramic coating on the surface of the nickel-chromium alloy bonding layer. The spraying process parameters are: plasma gas argon flow rate 47slpm, plasma gas hydrogen flow rate 8slpm, current 670A, power 47kW, powder carrier gas The argon flow rate is 4 slpm, the powder feeding rate is 40g/min, and the spraying distance is 115mm. In addition to the above atmospheric plasma spraying, explosive spraying or supersonic flame spraying can also be used. The thickness of the composite ceramic coating is 420-440 μm. The polished cross-sectional morphology of the corresponding coating shows that the coating has low porosity and high density, and the interface between the ceramic coating, nickel-chromium alloy layer and stainless steel substrate is well bonded (see Figure 3).

The composition analysis of the prepared alumina-yttrium oxide composite ceramic coating showed that the mass fraction of α-Al ₂ O ₃ phase was 15%, the mass fraction of γ-Al ₂ O ₃ phase was 37%, and the mass fraction of cY ₂ O ₃ phase was Fraction is ₂₉ %, _mY2O3 phase mass fraction is ₉ %, _Y3Al5O12 phase mass fraction is ₄ %, _Y4Al2O9 phase mass fraction is ₄ %, _YAlO3 phase mass fraction is ₂ % . The aluminum oxide coating and aluminum oxide-yttrium oxide composite ceramic coating square specimens were subjected to thermal shock tests. The specific conditions were: 500°C for 30 minutes and then water quenching for a total of 40 times. After 40 repeated thermal shocks, the alumina-yttrium oxide composite ceramic coating has no cracking or peeling off. However, the single alumina coating peeled off after only 6 thermal shocks, and the peeling area increased significantly after 40 thermal shocks (see Figure 5). Therefore, the alumina–yttrium oxide composite ceramic coating has better thermal shock resistance, which indicates its higher fracture toughness and bonding strength.

Further, the wear resistance of alumina-yttria composite ceramic coatings under high load conditions was investigated. The friction and wear test conditions are the same as in Example 1. The test results show that the friction coefficient of the alumina-yttria composite ceramic coating/graphite friction pair is low and the numerical stability is good, with an average value of μ=0.066, which is significantly better than that of the single alumina coating (see Figure 7).

Example 3

Thermal spraying aluminum oxide-yttrium oxide composite ceramic coating and preparation method thereof, the method comprises the following steps:

(1) Pretreatment of the metal substrate, including: roughening and purification of the pre-sprayed surface of the metal substrate. The metal substrate selection and pretreatment method are the same as in Example 1. The average surface roughness Ra of the stainless steel substrate after pretreatment is 8.19 μm;

(2) Aluminum oxide-yttrium oxide composite ceramic coating is deposited on the surface of the treated metal substrate by thermal spraying process

The preparation method of selecting the composite powder is the same as that of Example 1, except that the mass fraction of yttrium oxide powder is 20%. The nickel-aluminum alloy stress transition layer is first sprayed on the surface of the treated 2Cr13 stainless steel substrate. The particle size distribution range of the alloy powder is 35-55 μm. The plasma spraying process is adopted. The specific parameters are as follows: plasma gas argon flow rate 65slpm, plasma gas hydrogen The flow rate is 12slpm, the current is 560A, the power is 45kW, the powder delivery carrier gas argon flow rate is 3.5slpm, the powder delivery rate is 25g/min, and the spraying distance is 125mm. In addition to the above atmospheric plasma spraying, vacuum plasma spraying, supersonic flame spraying, etc. can also be used. The thickness of the nickel-aluminum alloy layer is 60-80 μm. Then plasma spray alumina-yttrium oxide composite ceramic coating on the surface of the nickel-aluminum alloy bonding layer. The spraying process parameters are: plasma gas argon flow rate 49slpm, plasma gas hydrogen flow rate 7slpm, current 680A, power 48kW, powder delivery carrier gas The argon flow rate is 3.5slpm, the powder feeding rate is 37g/min, and the spraying distance is 105mm. In addition to the above atmospheric plasma spraying, explosive spraying or supersonic flame spraying can also be used. The thickness of the composite ceramic coating is 440-460 μm. The polished cross-sectional morphology of the corresponding coating shows that the coating has low porosity and high density, and the interface between the ceramic coating, the nickel-aluminum alloy layer and the stainless steel substrate is well bonded (see Figure 3).

The composition analysis of the prepared alumina-yttrium oxide composite ceramic coating showed that the mass fraction of α-Al ₂ O ₃ phase was 24%, the mass fraction of γ-Al ₂ O ₃ phase was 53%, and the mass fraction of cY ₂ O ₃ phase was The fraction is 13%, the mY ₂ O ₃ phase mass fraction is 4%, the Y ₃ Al ₅ O ₁₂ phase mass fraction is 2%, and the Y ₄ Al ₂ O ₉ phase mass fraction is 4%. The room temperature thermal diffusivity and thermal conductivity of alumina coatings and alumina-yttrium oxide composite ceramic coatings were measured by laser scintillation method. The data show that composite ceramic coatings have better thermal conductivity than single alumina coatings (see Image 6). This will facilitate the service of the coating under harsh working conditions.

Further, the wear resistance of alumina-yttria composite ceramic coatings under high load conditions was investigated. The friction and wear test conditions are the same as in Example 1. The test results show that the friction coefficient of the alumina-yttria composite ceramic coating/graphite friction pair is low and the numerical stability is good, with an average value of μ=0.078, which is significantly better than that of the single alumina coating (see Figure 7). Meanwhile, compared with the alumina coating/graphite friction pair, the alumina–yttria composite ceramic coating/graphite friction pair showed a lower wear rate regardless of the coating or graphite (see Fig. 8).

Comparative example 1

In order to fully illustrate the performance superiority of the thermal sprayed alumina-yttrium _oxide composite ceramic coating of the present invention, a single _Al2O3 coating was also prepared as a comparative example, and the preparation method was the same as in Example 1, except that: Only pure alumina powder is used as spraying material. The thickness of the Al ₂ O ₃ coating is 440-450 μm, and the thickness of the nickel-chromium alloy stress transition layer is 65-75 μm. The coated grinding rings prepared in Example 1, Example 2, Example 3 and Comparative Example 1 were respectively paired with graphite blocks of the same material to investigate the tribological behavior of the coated friction pair under high load conditions. The friction and wear test method is the same as that described in Example 1. The results showed that compared with the single alumina coating, the alumina–yttrium oxide composite ceramic coating showed a lower coefficient of friction, better stability of the coefficient of friction, and a lower wear rate of the coating and graphite (see Fig. 7 and Fig. Figure 8). This is due to the better thermal shock resistance and thermal conductivity of the composite ceramic coating (see Figure 5 and Figure 6), indicating that the composite ceramic coating has higher strength and toughness.

Comparative example 2

The mass fraction of yttrium oxide powder in the composite powder was selected as 60%, and the alumina-yttria composite ceramic coating was prepared by thermal spraying, and the preparation method was referred to Example 1. The thickness of the composite ceramic coating is 450-460 μm, and the thickness of the nickel-chromium alloy stress transition layer is 60-70 μm. The composition analysis of the prepared alumina-yttrium oxide composite ceramic coating showed that the mass fraction of α-Al ₂ O ₃ phase was 10%, the mass fraction of γ-Al ₂ O ₃ phase was 27%, and the mass fraction of cY ₂ O ₃ phase was Fraction is 40%, _mY2O3 phase mass fraction is ₁₂ %, _Y3Al5O12 phase mass fraction is _{4 %} , _Y4Al2O9 phase mass fraction is ₄ %, _YAlO3 phase mass fraction is ₃ % , and under the same wear test conditions, the friction coefficient obtained by pairing the composite ceramic coating with graphite is significantly larger, with an average value of μ = 0.235, and the numerical stability becomes poor (see Figure 10), which is mainly due to excessive oxidation Yttrium significantly reduces the hardness of the composite ceramic coating. In addition, the thermal expansion coefficient of yttrium oxide changes greatly with the increase of temperature. When the content of yttrium oxide is too high, this large thermal expansion coefficient change will lead to the initiation and expansion of cracks at the phase interface of the coating, which is not conducive to the improvement of the wear resistance of the coating. .

Although the present invention has been disclosed as above with the preferred embodiment, it is not intended to limit the present invention, and any person skilled in the art can use the methods disclosed above and technical content to analyze the present invention without departing from the gist and scope of the present invention. Possible changes and modifications are made in the technical solution. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention, which do not depart from the content of the technical solution of the present invention, all belong to the technical solution of the present invention. protected range.

Claims (7)

1. An aluminum oxide-yttrium oxide composite ceramic coating is characterized in that, the aluminum oxide-yttrium oxide composite ceramic coating is directly obtained by mixing the aluminum oxide powder and the yttrium oxide powder uniformly through a drum type machine The composite powder is formed on the substrate by thermal spraying or on the stress transition layer located on the surface of the substrate. The mass fraction of the yttrium oxide powder is 20% to 40% of the composite powder, and the particle size is 15 to 40%. 45 μm, the particle size of the alumina powder is 15-45 μm; the substrate is a metal substrate, stainless steel substrate, alloy substrate or metal matrix composite material, and the alumina-yttria composite ceramic coating Including α-Al ₂ O ₃ phase, γ-Al ₂ O ₃ phase, cY ₂ O ₃ phase, mY ₂ O ₃ phase and Y _x Al _y O _z phase generated in situ from alumina and yttrium oxide, the Y _{xAl y O z} is Y ₃ Al ₅ O ₁₂ , Y ₄ Al ₂ O ₉ and/or YAlO ₃ , wherein the mass ratio of α-Al ₂ O ₃ phase to γ-Al ₂ O ₃ phase is 1: (2～ 3); the stress transition layer is nickel-chromium or nickel-aluminum alloy with a thickness of 40-100 μm; the thickness of the alumina-yttria composite ceramic coating is 250-500 μm; the thermal spraying is plasma spraying, plasma Spraying process parameters are: plasma gas argon flow rate 40~50slpm, plasma gas hydrogen flow rate 6~10slpm, current 630~690A, power 45~50kW, powder carrier gas flow rate 3~4slpm, powder feeding rate 30~40g/ Minutes, spray distance 100 ~ 120mm. 2. The alumina-yttria composite ceramic coating according to claim 1, characterized in that the mass fraction of the α-Al ₂ O ₃ phase is 9-24%. 3. The alumina-yttria composite ceramic coating according to claim 1, characterized in that the mass fraction of the cY ₂ O ₃ phase is 9-29%, and the mY ₂ O ₃ phase and cY ₂ O ₃ The mass ratio of the phases is 1: (3-4). 4. The alumina-yttria composite ceramic coating according to any one of claims 1-3, wherein the mass fraction of the _{YxAlyOz phase} is _6-10 %. 5. A method for preparing alumina-yttrium oxide composite ceramic coating according to any one of claims 1-4, characterized in that, comprising: (1) Pretreat the substrate, including roughening and purifying the pre-sprayed surface of the substrate; (2) Mix the alumina powder and yttrium oxide powder uniformly through a drum machine to obtain a composite powder; (3) Deposit the composite powder obtained in step (2) on the surface of the pretreated substrate obtained in step (1) by using the plasma spraying to obtain the alumina-yttria composite ceramic coating; or deposit the composite powder Before the material, the stress transition layer is sprayed on the surface of the pretreated substrate obtained in step (1), and then the composite powder obtained in step (2) is deposited on the stress transition layer by plasma spraying to obtain the alumina-oxidized Yttrium composite ceramic coating. 6 . The preparation method according to claim 5 , wherein the surface roughness Ra of the roughened substrate is 5-10 μm. 7. The preparation method according to claim 5 or 6, characterized in that the powder particle size distribution range of the stress transition layer in step (3) is 35-65 μm, and the sprayed stress transition layer is plasma sprayed , The plasma spraying process parameters are: plasma gas argon flow rate 50~70slpm, plasma gas hydrogen flow rate 8~12slpm, current 550~620A, power 40~45kW, powder carrier gas argon flow rate 3~4slpm, powder feeding rate 20 ～30g/min, spraying distance 110～130mm.